Some wireless communication systems (in particular many highly evolved communication systems) apply relaying functionality. One example of such a system is a system that operates according to LTE-Advanced (Long Term Evolution Advanced) advocated by 3GPP (3rd Generation Partnership Project) and targeting to meet the requirements of the International Telecommunications Union (ITU) for next generation mobile systems (IMT-Advanced). Relaying functionality have been discussed (among other technology components for such systems) in 3GPP, RP-080236, REV-080060, Report of 3GPP TSG RAN IMT Advanced Workshop, Shenzhen, China, Apr. 7-8, 2008, and in Ericsson, R1-082024, “A discussion on some technology components for LTE-Advanced”, contribution to TSG-RAN WG1 #53.
There exists a plethora of options for relaying functionality, e.g.                Layer 1 relay (repeater) as described in Ericsson, R1-082470, “Self backhauling and lower layer relaying”, contribution to TSG-RAN WG1 #53 bis,        Type one relay as described in the 3GPP standard, and        Type two relay as described in Vodafone, CMCC, Huawei, Ericsson, et al, R1-091632, “Type II relay frame-work definition”, contribution to TSG-RAN WG1 #56bis.        
FIG. 1 is a schematic drawing illustrating part of an example network setup employing relays. A base station site 110 comprises a base station 111 associated with a so called donor cell 115. The base station 111 may be any applicable base station, for example an eNodeB (evolved NodeB). The base station 111 may be connected to a network controller 140 and to the rest of the example network. The donor cell 115 is serving or camping cell for the terminals 112, 113, 114. Communication between the base station 111 and the terminals 112, 113, 114 takes place over the base station access link represented by arrows 119 (downlink, DL, and uplink, UL).
The base station 111 of the donor cell 115 is associated with two relay sites 120 and 130, each comprising a relay 121 and 131 respectively.
The relay 121 may be any applicable relay, for example a type one relay. The relay 121 is associated with a cell 125. The cell 125 is serving or camping cell for the terminals 122, 123. Communication between the relay 121 and the terminals 122, 123 takes place over the relay access link represented by arrows 128 (downlink, DL, and uplink, UL), while communication between the relay 121 and the base station 111 takes place over the relay backhaul link represented by arrows 129 (downlink, DL, and uplink, UL).
The relay 131 may be any applicable relay, for example a type one relay. The relay 131 is associated with three cells 135, 136, 137. The cell 137 is serving or camping cell for the terminal 132. Communication between the relay 131 and the terminal 132 takes place over a relay access link (not shown), while communication between the relay 131 and the base station 111 takes place over a relay backhaul link (not shown).
Relaying is considered for LTE-Advanced as a tool to improve e.g. the coverage of high data rates, group mobility, temporary network deployment, the cell-edge throughput, and/or to provide coverage in new areas. At least the type one relay node functionality is a part of LTE-Advanced.
A type one relay node may control one or several cells, each of which has a unique physical-layer cell identity and appears to a terminal as a separate cell, distinct from the donor cell. The same RRM (Radio Resource Management) mechanisms are available at both the eNodeB and the type one relay. Typically, cells controlled by a type one relay may have the additional requirement that they should be able to support also LTE Rel-8 terminals.
A relay node is typically wirelessly connected to the radio access network via a donor cell as described in connection to FIG. 1. The radio link between the base station (eNodeB) of the donor cell and the relay node is termed the relay backhaul link. The radio link between the relay node and a terminal associated with the relay node is termed the relay access link.
The connection of a terminal to the radio access network (via a relay node) can he either in-band or out-band depending on, for example, the applied communication standard and other parameters and/or conditions as specified by a communication standard or an operator of the network.
In the case of in-band relaying, the relay backhaul link operates in the same frequency spectrum as the relay access link. Thus, if no measures are taken, there is a risk that there will be severe output-to-input interference at the relay node if the relay transmits and receives simultaneously. One solution to this obstacle is to time multiplex the relay backhaul link and the relay access link. One implementation of this solution comprises introducing one or more “backhaul” sub-flumes dedicated for relay backhaul transmission.
In LTE-Advanced such an implementation may include scheduling relay access uplink transmissions and relay backhaul uplink transmissions in different sub-frames. Furthermore, MBSFN (Multimedia Broadcast over a Single Frequency Network) sub-frames may be used to facilitate relay backhaul downlink transmissions in LTE-Advanced. In that case, the performance of relay backhaul downlink transmissions can be guaranteed by not allowing any relay access downlink transmissions except in a few OFDM symbols (e.g. the first one or two OFDM symbols where control signalling is transmitted). The set of relay backhaul uplink and/or downlink sub-frames (i.e. sub-frames during which relay backhaul transmissions may occur) may be semi-statically assigned.
FIG. 2 illustrates a situation where MBSFN sub-frames 210, 220 are used for downlink transmissions in relation to a relay node. Each of the sub-frames 210, 220 comprises a control part 211, 221 and a data part 212, 222. The sub-frame 210 may be used for relay access downlink transmissions in a conventional manner, while the sub-frame 220 may be used for relay backhaul downlink transmissions. Relay access downlink transmissions may be allowed in sub-frame 220, but only in the first part 221 of sub-frame 220. Thus, in this case there are no relay access downlink transmissions in the time interval 223, and relay backhaul downlink transmissions may be received without output-to-input interference at the relay node.
The relay backhaul links (each associated with a respective relay node) and the base station (e.g. eNodeB) access link may be time multiplexed or frequency multiplexed with respect to each other.
As mentioned above, relaying may be introduced to a system to improve e.g. the coverage of high data rates, group mobility, temporary network deployment, the cell-edge throughput, and/or to provide coverage in new areas. These objectives can only be achieved with adequate radio resource allocation to the various links.
The issue of radio resource allocation in relaying systems have been discussed in Dai Qin-yun, Rong Lu, Hu Hong-lin, Su Gang, “Resource allocation using time division multiple access over wireless relay networks”, The Journal of China Universities of Posts and Telecommunications, 2008, 15(3), in Kaneko M., Popovski P., Hayashi K., “Throughput-Guaranteed Resource-Allocation Algorithms for Relay-Aided Cellular OFDMA System,” VTC, May 2009, and in US 2009/0163220 A1 (Chin Ngo, Yong Liu, “Method and system for resource allocation in relay enhanced cellular systems”).
In a system with relay functionality it is a difficult task to adequately optimize allocation of radio resources to each of the relay access links, each of the relay backhaul links and the base station access link.
There is a need for alternative (and preferably improved) methods and arrangements for radio resource allocation of wireless communication systems comprising at least one network node and at least one relay associated with the network node.